Lipids and Membrane Structure Quiz

Lipids

• Lipids are biological compounds insoluble in water but soluble in organic solvents (ether, benzene, acetone, chloroform).
• Lipids are synonymous with fats but also include phospholipids, sterols, etc.
• Lipids have a chemical structure of glycerol plus fatty acids.
• The ester bond is (O-C=OR).

Functions of Lipids

• Lipids are concentrated sources of energy (9.45 kcal/g), more than double the energy provided by protein or carbohydrate.
• They provide essential fatty acids which the body cannot produce and are critical for children's growth and brain development, and skin health.
• Lipids are a source of phosphorus through phospholipids.
• Lipids provide fat-soluble vitamins (A, D, K, E).
• Lipids act as insulators under the skin, protecting internal organs like the heart and kidneys.
• Lipids are important for vitamin D production.

Lipid Classes

• Simple: Fatty acids esterified with glycerol (neutral fats, triglycerides, fats, oils, and waxes).
• Compound: Same as simple lipids, but other attached compounds.
  • A-Phospholipids: Fats containing phosphoric acid and nitrogen.
  • B-Glycolipids: Fatty acids compounded with carbohydrate (CHO), but no nitrogen.
  • Derived Lipids: Substances from the above derived by hydrolysis.
• Sterols: Large molecular weight alcohols found in nature, often combined with fatty acids (e.g., cholesterol).

Fatty Acids

• Fatty acids are composed of a carboxylic acid "head group" and a long hydrocarbon "tail".
• Typically, the hydrocarbon tail has an even number of carbon atoms.
• Hydrocarbon tails can be saturated or unsaturated. Unsaturated tails have one or more double bonds.
• Common and systematic nomenclatures are used to describe fatty acids. (e.g., stearic acid or octadecanoic acid (CH3(CH2)16COOH)).

Saturated vs. Unsaturated Fatty Acids

• Saturated: Have no double bonds between carbons in the chain (e.g., palmitic acid CH3(CH2)14COOH).
• Polyunsaturated: Have more than one double bond in the chain (e.g., linoleic acid).

Essential Fatty Acids

• Essential fatty acids are not synthesized in the body in sufficient amounts.
• Linoleic and linolenic acids are essential for humans and are easily obtained from plant and fish oils.
• Examples are linoleic acid CH3(CH2)4(CH=CHCH2)2(CH2)6COOH and linolenic acid CH3CH2(CH=CHCH2)3(CH2)7COOH.

Non-Essential Fatty Acids

• Synthesized within the body.
• Example, oleic acid CH3(CH2)7CH=CH(CH2)7COOH

Triacylglycerols (Triglycerides)

• Triesters of long-chain fatty acids and glycerol.
• Comprised of only one fatty acid on a glycerol backbone. Triglycerides that are solid at room temperature are called fats and are usually from animal sources. They are a high degree of saturated fatty acids.
• Triglycerides that are liquid at room temperature are called oils, usually from plant and fish sources, and high in unsaturated fatty acids.

Simple Lipid Reactions

• Esterification: Glycerol and fatty acids form triglycerides.
• Saponification: Production of carboxylate salts of fatty acids in triglycerides (soaps).
• Hydrogenation: Double bonds of unsaturated fatty acids are hydrogenated to produce margarines from oils.

Oxidation

• Oxidation happens to double bonds of fatty acids in fats and oils.

Compound Lipids

• Glycerophospholipids: Common constituents of cellular membranes (e.g., phospholipids and phosphatidates).

  • They have a glycerol backbone.

• Sphingolipids: (e.g. sphingomyelin)

• Contains various substituents like sphingosine

Steroids

• Non-hydrolyzable lipids.
• All steroids contain the cyclopentanoperhydrophenanthrene ring system.

Cholesterol

• An important constituent of cell membranes, with a short hydrocarbon tail.
• Largely hydrophobic, but has a hydroxyl group making it amphipathic (both water-loving and fat-loving).
• Cholesterol inserts into bilayer membranes, with the hydroxyl group oriented towards the aqueous phase, and hydrophobic ring system adjacent to fatty acid chains.

Wax

• Composed of a long-chain fatty acid bonded to a long-chain alcohol.
• Forms protective coverings (e.g., plant surfaces, animal ears, skin, and hair).
• Insoluble in water and not easily hydrolyzed.
• Often found in protective coatings.

Test your knowledge on the functions and structures related to lipids in biological systems. This quiz covers various aspects such as phospholipids, fat-soluble vitamins, and the role of cholesterol in membrane structures. Understand the importance of lipids in energy and body protection.